1. Field of the Invention
The present invention relates generally to computerized data communications systems, and more specifically to a computer system for monitoring a plurality of remote electrically operated devices such as slot machines wherein the data bus incorporates the electrical power lines supplying the remote devices.
2. Background of the Invention
A generation ago many computer experts were of the opinion that a handful of general purpose digital computers would satisfy all the computing needs of the United States (and presumably the world). Today we have hand-held programmable calculators and home computers, and the commercial and industrial use of a central computer to monitor and control a plurality of remote electrical devices has become commonplace. The remote devices may be geographically dispersed (e.g. computer terminals in vaarious cities), or may be relatively proximate one another in a single building (e.g. heating and ventilation controls). The common denominator is information transfer, regardless of whether the information is to be used for accounting, security, energy conservation, or some other purpose.
One known and commonly used way of transferring data is to encode the data bits as a series of phase shifts that are superimposed on a carrier signal. This technique, known as phase shift keying, is most often carried out by having the transmitter constantly sending the carrier signal so that the receiver can remain in constant synchronization. Needless to say, this cannot be done if two-way communication is to be carried out over the same telemetry lines. In such a case, separate clocks at the transmitter and receiver are maintained in constant synchronization during data transmission by means of a phase locked loop which derives its timing from the bit changes themselves. The use of a phase locked loop is less than optimal since it requires a considerable amount of critically designed circuitry and involves a significant amount of lockup time in order to synchronize the clocks. Moreover, when the environment is noisy, a spurious signal has the effect of throwing the phase locked loop out of lock so as to destroy the data, even if the spurious signal itself didn't represent a threat to data integrity.
Slot machines are but one example of devices whose operation is characterized by substantial cash flow and thus present accounting and security problems. In the context of a gambling casino, a large number of machines are located in a room which is accessible to the public at all times. Each machine is characterized by a payout ratio that is slightly less than one hundred percent so that on the average the casino retains a small share of the total money passing through the machines. Overall profitability depends on having a large number of slot machines operating twenty-four hours a day, seven days a week, so that the effects of statistical anomalies are eliminated and the small percentage retained by the casino is applied to a large base to provide a large positive cash flow increment.
Slot machines are, for the most part, relatively complex electromechanical devices. Even minor malfunctions can result in substantial changes in the payout ratio, thus rendering the machines non-profitable, or even worse, cash drains. In addition to malfunctions of an accidental sort, there are those malfunctions caused by intentional tampering with the machine mechanism. Such tampering methods and their manifestations are well known to those in the slot machine art, and all too well by those engaged in the larcenous activities. Given the large amounts of cash involved, small systematic cash diversion, typically too small to be detected by casino management, is nevertheless attractive to the would be wrongdoers.
Mindful of the desirability of remotely monitoring the cash flow characteristics of a plurality of slot machines, there have been proposed security and monitoring systems including a central computer in communication with individual sensor units within the slot machines. Data transfer occurs along dedicated telemetry lines, thus providing reasonably high data integrity.
Unfortunately, the use of dedicated telemetry lines has the significant disadvantage that providing such dedicated lines represents a significant expense. Moreover, if it is desired to retrofit a roomful of slot machines with such a security system, the installation of the data lines is intolerably disruptive. Aside from the fact that each machine is required to be inoperative for the installation of its sensor unit, the operation of large groups of machines must be suspended for considerable intervals while the telemetry lines are being installed. As mentioned above, slot machine profitability depends on the operation of the machines on a substantially continuous basis. Therefore, the cost of suspending operation of large numbers of machines for even several hours represents a substantial disincentive to retrofit the machines in the first place.
Consequently, in spite of the demonstrable need for remote slot machine monitoring systems, the costs involved in retrofitting a roomful of slot machines with such a system has tended to hinder the development and implementation of remote slot machine monitoring systems.